Method and apparatus for roasting ores



March 31, 1936. v FOWLER, JR 2,035,699

METHOD AND APPARATUS FOR ROASTING ORES Filed Dec. 19, 1931 iNVENTOR 77/4 Pow/er, (/7:

ATTORNEY Patented Mar. 31, i936 PATENT OFFICE:

METHOD AND APPARATUS FOR ROASTING ORES Theodore V. Fowler, Jr., Pelham, N. Y., assignor to General Chemical Company, New York, N. Y., a corporationof New York Application December 19, 1931, Serial No. 582,082

20 Claims.

' One particular application of the inventionlies in the roasting of zinc sulfides, such as finely divided zinc sulfide flotation concentrates. Broadly speaking, the invention contemplates a method including the preliminary phases of bed roasting v with respect to the initial drying of the ore and heating the same to the ignition temperature, to-

' gether with the principles of suspension roasting.

Bed roasting and suspension roasting of su1- fide ores are known in the art. Bed roasting of finely divided sulfide ores has been widely practiced, for example, in the well known Herreshoff roasters. However, with respect to certain types of sulfide ores, such as zinc sulfides, and iron sulfides such as pyrrhotite, which contain comparatively small quantities of sulfur, difficulty in obtaining a good roast is often experienced because of insufiicient available heat and it is often necessary in order to obtain reasonably satisfactory results to supply heat from extraneous sources to complete the roasting operation.

' Hence, it has been usual to carry out the roasting of zinc sulfides in furnaces equipped with muflled hearths in which producer or other combustible gas is burned for the purpose of supplying the required additional amounts of heat. Muiiied hearth furnaces are themselves expensive to build, and the construction and upkeep of gas producers are large items of expense. A further disadvantage encountered in the roasting of zinc ores in hearth furnaces isthat although high temperatures are desirable in the final stages to complete desulfurization, such high temperatures are not ordinarilyobtainable without the supply of extraneous heat, and when extraneous heat is supplied to eifect complete desulfurization the destructive effects on the rabbling mechanism become pronounced thus shortening the life of the roasting equipment and increasing production costs.

To overcome many of the difiiculties oi hearth roasting arising chiefly out of expensive equipment, suspension roasting has been proposed. However, when working with zinc sulfides the problem of supplying the additional heat again arises. Hence, it has been suggested to preheat the air used to form the gaseous suspension and support combustion, and to preheat the ore, or preheat both air and ore, the purpose being to raise the temperature of the ore to such an extent that on introduction of the suspension into the combustion chamber, the ore is heated to approximately the ignition point. In practice, however, such preheating to raise the-temperature of the ore to the ignition point has not been obtain- 5 able economically. Preheating the air has not been particularly successful, since the contact of the ore and air prior to the introduction of the suspension in the roasting chamber is so brief that the ore is not sufliciently heated. Preheating the ore raises a most important difficulty in providing suitable apparatus for conveying ores heated to temperatures in the neighorhood of 1000" F. or above, and for forming a gaseous suspension of such comparatively hot ore in air in a suitable mixing nozzle. Hence, the principal disadvantage in desulfurizing ores such as zinc sulfides in bed roasting is an incomplete roast, and with respect to suspension roasting, the difficulty lies in preheating the ore sufliciently so that ignition will ensue immediately following the introduction of the suspension in the roasting chamber.

The principal object of the present invention lies in the provision of a method and apparatus for suspension roasting of sulfide ores whereby the preheating of the ore to the ignition.temperature on introduction into the roasting chamber is assured. According to'the invention, the finely divided ore is subjected to preheating in an operation embodying the preliminary phases of bed roasting with respect to the initial drying of the ore and raising the temperature of the same to the ignition point. Such preheating is preferably carried out in an atmosphere of the hot gaseous products of combustion of the final suspension roasting. The ore, heated in this manner to, or substantially to, the ignition temperature,i is 'fed into a roasting chamber preferably so that ignition of the ore takes place substan- 40 tially immediately upon introduction of the ore into the roasting chamber, and-combustion of the ore proceeds in a suspension of the ore in oxidizing gasin the roasting chamber. The invention is of particular value in the roasting of ores which customarily do or may require the application 01' extraneous heat to accomplish complete roasting. 2

Further objects of the invention and advantages therof will appear from the following description taken'in connection with the accompanying drawing illustrating partly in section and partly in elevation one embodiment ofa roasting furnace particularly adapted forcarrying out the invention. g 56 Referring to the drawing, the apparatus includes principally a shaft roaster and a multihearth heater indicated generally by the reference numerals I0 and H. The shaft roaster comprises a vertically elongated, preferably cylindrical combustion chamber |2 within a steel shell |3 lined with refractory material 4. The shaft roaster is supported by a frame l5, and suitable brickwork l6. The lower end of the combustion chamber is cone-shaped, forming a cinder pit l8 discharging into a cinder outlet l9 equipped with any approved form of gate. The shaft roaster is held in place laterally by structural framework 2|. Spaced about the circumference of the combustion chamber are air inlets 22. The discharge ends of the inlet passages are horizontally elongated, as indicated at 23, so as to cause introduction of air or other oxidizing gas into the combustion chamber in the form of a series of more or less fiat sheets. Any required number of inlets 22 may be provided at desirable vertical intervals. In the embodiment of the invention disclosed three sets are illustrated. Air is supplied to the inlets 22 through bustle pipes 25, the inlets 26 of which open into' an air inlet main 21.

The hearth heater II is positioned directly above the shaft roaster and rests upon a platform 30, the weight of the hearth heater and associated mechanism being carried by the structural framework 2|. prises a heating chamber, indicated generally by the reference numeral 3|, formed by vertical cylindrical walls 32. the drying deck 33 and the lowermost hearth 34. The heater includes additional intermediate hearths 36 and 31. Ore inlets 38 extend through drying deck 33 adjacent walls 32 and openings 40 pass through hearth 31 around the periphery thereof. Hearth 36 is provided with a central ore and gas passage 4|. The lowermost hearth 34 serves as the upper end of the combustion chamber |2 of the shaft roaster, and includes a centrally disposed passage 43, and a plurality of openings 44 passing through the hearth 34 intermediate the periphery of the passage 43 and the inner surface of the refractory lining l4 of the shaft roaster.

The rabbling mechanism for the hearths is of the general construction employed in the well known Herreshoif roaster, and hence need not be described in detail. The rotatable shaft 46, having rabble, arms 41, is mounted in bearings 48 and 49, the weight of the rabbling mechanism being transmitted to the framework through cross-member 56 and bearing 49. Shaft 46 has therein a longitudinal conduit 52 extending to bearing 48, and through which cooling air is passed into the rabble arms. The arrangement is such that the cooling air leaves the rabbling arms 41 and the annular passage 55 by way of chamber 56 arranged in any suitable manner so as to permit rotation of the shaft 46 and conduit 52. Ore from a hopper 511s fed intermittently onto the drying deck 33 by a sweep fixed to shaft 46. The ore supply in hopper 51 may be maintained by a conveyor not shown.

The gaseous products of the entire roasting operation leave the apparatus through the gasv The hearth heater com-- locks 1|.

Air for use both in the roasting operation and as a cooling medium in the rabbling mechanism is supplied through an air inlet 13. Part of the air flows through the pipe 14 into the central conduit 52 in the shaft 46, and another part is passed through chamber 15, thus serving to cool the lower bearing of shaft 46. Air for the entire roasting operation is preheated by circulating the same around cones 65 in chamber 16, and is then conducted into combustion chamber l2 through pipe 21. A by-pass 11, controlled by valve 18, is disposed between the upper end of chamber I2 and the outlet conduit 6| to facilitate control of the quantity of hot gases passing 5- through heating chamber 3| thus permitting regulation of the temperature therein. The degree of preheating of the air entering chamber l2 may be regulated by valve-controlled by-pass 80.

The roasting operation is carried out substantially as follows: Finely divided sulfide ore, such as zinc sulfide flotation concentrates, is

continuously charged into hopper 51 from which small quantities are intermittently swept onto the surface of the deck 33 on which excess moistureis removed from the ore by heat radiating from the roasting chamber 3|. It will thus be seen that, according to the present method, comparatively wet concentrates may be employed, whereas in prior suspension roasting, it has been necessary to provide additional apparatus for drying the ore before charging the same in the form of a. gaseous suspension into the combustion chamber. As is known in the art, the plows on the uppermost rabbling arm are so arranged as to slowly feed ore through the passages 38 to the hearth 36. Drying is furthered and preheating is commenced to some extent on the hearth 36 over which the ore is gradually worked toward and discharged through the central opening 4| to the intermediate hearth 31. As the ore passes over the upper hearths, the temperature of the ore is gradually increased, until by the time the ore is discharged through passages 46 onto the lowermost hearth 34, preheating is well initiated, and the temperature of the ore approaches the ignition point. During'the inward movement of the ore over lower hearth 34, the temperature is further raised, and when the ore is discharged into the upper end of the shaft roaster through openings 43 and passages 44, the temperature of the ore is substantially at the ignition point, for example around 1400-1600 F. It will be seen that on account of the particular arrangement of central opening 43 and the several passages 44, the ore is fed from the hearth 34 into the shaft roaster in a shower resembling two concentric cylinders, thus facilitating the formation of a suspension of the ore in an oxidizing gas in the shaft roaster.

Air in quantities necessary to supply oxygen for the entire roasting operation is introduced into the shaft roaster through the several inlets 22, and rises through chamber I2, countercurrent to e of the burning ore. This upward movement of air effects the formation of a suspension of the finely divided ore, and further serves to retard suillciently the descent of any heavier particles of ore to facilitate complete desulfurization.

The temperature of the ore on the lower hearth 34 may be at or possibly slightly above the ignition temperature, and hence, combustion of the ore particles takes place almost instantaneously upon the introduction of the ore into the upper end of the shaft master. Since ignition is immediately brought about, desulfurization proceeds rapidly, and is completed in the central zone of chamber l2, considerably before the ore particles fall into the cinder pit in. Accordingly, on account of the high temperatures easily attainable in shaft roasting, complete desulfurization is assured. The sulfur dioxide gases from the shaft roaster, at temperatures around 1800-2000" F,,

enter the upper chamber Ii through the opening 43, pass successively over'the, heart and are withdrawn from the apparatus thro h conduit 6|. During'passage through chamber ii, the hot gases are in direct contact with the ore on the several hearths, thus effecting drying and preliminary heating of the ore and positively raising the temperature thereof to about the ignition point. In the event that the temperature in chamber 3! should become undesirably high, necessary quantities of hot gases from chamber l2 may be by-passed around chamber 3| through pipe II by suitable regulation of'valve 10.

The advantages arising from the invention are numerous. Primarily, the temperature of the ore on introduction into the roasting chamber l2 may be at or around the ignition point, so that combustion is instantaneously initiated. High finishing roasting temperatures are easily attainable in the combustion chamber. with the result that the ore is completely desulfurized and no equipment having moving parts is damaged because of the high temperatures. Additional heat, beyond that generated in the roasting operation as a whole, is not required. Wet ore or concentrates may be used at the start. thus avoiding the necessity of additional drying apparatus particularly where wet concentrates are employed. The necessity of handling hot preheated ore in specially designed conveying apparatus is avoided. The invention further makes available, in the roasting of sulfide ores, such as zinc-sulfides, pyrrhotite, pyrites, etc., the full economic benefits of suspension roasting, and additionally assures heating of the ore to ignition temperature Just prior to introduction into the ,shaft roaster by reason of the preliminary direct contact of the ore and the highly heated eiiiuent gases of the suspension,

rusting stage.

I claim:

1. The process of roasting finely divided sulfide ores which comprises heating the ore in a bed heating operation by feeding the ore in centercurrent fiow with hot gaseous combustion prodnets of a succeeding roasting operation, and then feeding the ore into a combustion chamber and roasting the ore in suspension in an oxidizing gas.

2. The process of roasting finely divided sulfide ore which comprises a bed of the ore while heating the ore in an comprising the gaseous combustion products 'of a succeeding roasting stage to such extent that the temperatareoftheoreisraisedsubstantiallyto the ignition point, and then feeding the ore into 3 a combustion chamber and roasting the ore in suspension in an oxidizing gas to substantially complete desulfurization.

3. The process for roasting finely divided metal phere comprising hot gases from the succeeding roasting operation, and then feeding the fines into a combustion zone constituting the roastns sta e. in suspension in oxidizing gas to produce sulfur dioxide gases and oxide cinder, recovering sulfur dioxide gases from the roasting stage, and dis charging cinder therefrom.

4.- The process for roasting finely divided metal sulfides in an operation involving a heating stage and a roasting stage in which the sulfide fines are burned in an oxidizing gas which process comprises maintaining a bed of fines in the heating stage, passing'the fines forming the bed through the heating stage while agitating the fines and heating the same in an atmosphere comprising hot gases from the succeeding roasting operation passing through the heating sta e, and then feeding the fines into a combustion zone constituting the roasting stage, roasting the fines in said zone while in suspension in oxidizing gas to produce sulfur dioxide gases and oxide cinder, recovering sulfur dioxide .gases from the roasting stage, and discharging cinder therefrom.

5. The process of roasting finely divided sulfide ores which comprises heating the ore by feeding the ore in countercurrent fiow with hot gaseous combustion products of a succeeding roasting operation, and then feeding the ore into a combustion chamber and roasting the main suspension in an oxidizing gas.

6. The process of roasting finelydivlded sulfide ore which comprises heating a bed of the ore to such extent that the temperature thereof is raised substantially to the ignition point, and then feeding the ore into a combustion chamber and roasting the ore thereinto substantially complete desurfurization while maintaining the ore in suspension in an oxidizing gas flowing countercurrent to the movement of the roasting ore.

7. The process of roasting finely divided sulfide ore which comprises agitating a bed of the ore while heating the ore in an atmosphere compris ing the gaseous combustion products of a succeeding roasting stage to such extent that the temperature of the ore is raised substantially to the ignition point, and then feeding the ore into a combustion chamber and roasting the ore therein to substantially complete desulfurization while maintaining the ore in suspension in an oxidizing gas flowing counter-current to the movement of the roasting ore.

roasting the fines in said zone while '15 8. The process of routing finely divided zinc sulfide ore which comprises heating the ore in a bed heating operation to such extent that the temperature of the ore is raised substantially to the ignition point, and then feeding the ore into a combustion chamber and roasting the ore therein to substantially complete desulfurization while maintaining the ore in suspension inan oxidizing gas flowing countercurrent to the movement of the roasting ore.

9. The process of roasting finely divided zinc sulfide ore customarily requiring the applwation of extraneous heat to effect substantially complete desulfurization which comprises heating the ore in a bed heating operation in an atmosphere comprising the gaseous combustion products of the succeeding roasting stage to such an extent that the temperature of the ore is raised substantially to the ignition point, and then feeding the ore into a combustion chamber and roasting the ore therein to substantially complete desulfurization while maintaining the ore in suspension in an oxidizing gas flowing countercurrent to the movement of the roasting ore.

10. Apparatus for roasting finely divided sulfide ore to efiect substantially complete desulfurization which comprises means for agitating a bed of the ore while heating the same, means for effecting such heating in an atmosphere comprising gaseous combustion products of a succeeding roasting stage, a combustion chamber, means for then feeding the ore into the combustion chamber, and means for forming in the combustion chamber a suspension of the ore in an oxidizing gas, whereby the ore is roasted to substantially complete desulfurization.

11. Apparatus for roasting finely divided metal sulfide in suspension in an oxidizing gas comprisinga vertically disposed roasting furnace comprising a sulfide fines heating chamber in the upper part of said furnace and a combustion chamber in the lower part of the furnace, a fines heating hearth in said heating chamber, means for maintaining on said hearth a bed of sulfide fines, means for causing said'bed of fines to pass over said hearth while agitating the fines during passage of the same over said hearth, means including a connection between the combustion chamber and the heating chamber for flowing hot gases from the combustion chamber over the bed of fines during passage of the bed of finesthrough the heating chamber, whereby said fines are heated in an atmosphere comprising hot gases of a succeeding roasting operation, means for inircducing fines after passage over said hearth into the combustion chamber and for forming therein a suspension of the fines in oxidizing gas whereby the fines are roasted to produce sulfur dioxide gases and oxide cinder, means for withdrawing sulfur dioxide gases from the combustion chamber, and means for discharging cinder therefrom.

12. Apparatus for roasting finely divided sulfide ore to effect substantially complete desulfurization which comprises means for agitating a bed of the ore while heating the same, means for effecting such heatng in an atmosphere comprising gaseous combustion products of a succeeding roasting stage, a combustion chamber, means for then feeding the ore into the combustion chamber. and means for forming in the combustion chamber a suspension of the ore in an oxidizing atmosphere comprisng means for passing through said chamber, counter to the movement of the ore, a current of oxidizing gas, whereby the ore is roasted to substantially completc desulfurization.

going heating thereon, a combustion chamber,

means forpassing ore from the bed into the combustion chamber in the form of a shower, and

means for passing through the chamber, counter to the movement of the ore therein, a stream of oxidizing gas, whereby the ore is roasted in the combustion chamber in gaseous suspension.

14. Apparatus for roasting ore comprising a chamber, a heating hearth in the chamber, means for feeding ore to the hearth, means for agitating ore on the hearth while undergoing heating thereon, a combustion chamber, means for passing ore from the hearth into the combustion chamber in the form of a shower, means for forming in the combustion chamber a suspension of the ore in an oxidizing gas, and means for conducting the gaseous products of combustion from the combustion chamber over the roasting hearth, whereby heat is imparted to the ore undergoing heating on the hearth, and the gaseous products ofv the entire roasting operation become intermingled.

15. Apparatus for roasting finely divided metal sulfide in suspension in an oxidizing gas comprising a vertically disposed roasting furnace comprising a sulfide fines heating chamber in the upper part of said furnace and a combustion chamber in the lower part of the furnace, a fines heating hearth in said heating chamber, means for maintaining on said hearth a bed of sulfide fines, means for causing said bed of fines to pass over said hearth while agitating the fines during passage of the same over said hearth, means including a connection between the combustion chamber and the heating chamber for flowing hot gases from the combustion chamber over the bed of fines during passage of the bed of fines through the heating chamber, whereby said fines are heated in an atmosphere comprising hot gases of a succeeding roasting operation, means for introducing fines after passage over said hearth into the combustion chamber and for forming therein a suspension of the fines in oxidizing gas, whereby the fines are roasted to produce sulfur dioxide gases and oxide cinder, means for heating said oxidizing gas prior to admission to said combustion chamber by heat generated in the roasting operation, means for withdrawing sulfur dioxide gases from the combustion chamber, and means for discharging cinder therefrom.

16. Apparatus for roasting ores comprising a vertically disposed shaft roaster having an opening at the upper end thereof, a heating hearth mounted above the shaft roaster, means for feeding ore to the hearth and means for agitating ore undergoing heating on the hearth, means for gradually feeding ore from the hearth into the upper end of the shaft roaster, and means for introducing oxidizing gas into the lower portion of the shaft roaster for forming a suspension of the ore in a counter current flow of oxidizing gas.

17. Apparatus for roasting ores comprising a vertically disposed shaft roaster having an opening at the upper end thereof, a chamber mounted directly above the shaft roaster, an outlet for the chamber positioned immediately above the opening in the shaft roaster, a plurality of heating hearths in said chamber, means for feeding ore to the uppermost of said hearths, means for gradually passing ore while agitating the same successively over the hearths, means for gradually discharging ore from the lowermost hearth into the upper end of the shaft roaster, and means for introducing oxidizing gas into the lower portion of the shaft roaster for forming a.

suspension of the ore in a counter current flow of oxidizing gas.

18, Apparatus for roasting ores comprising a vertically disposed shaft roaster having an opening at the upper end thereof, a chamber mounted directly above the shaft roaster, an outlet for the chamber positioned immediately above the opening in the shaft roaster, a plurality of heating hearths in said chamber, means for feeding ore to the uppermost of said hearths, means for gradually passing ore while agitating the same successively over the hearths, means for gradually discharging ore from the lowermost hearth into the upper end of. the shaft roaster in the form of a shower, means for passing upwardly through the shaft roaster a stream of oxidizing gas, whereby a suspension of the ore in the gas is formed, and means for passing the gaseous products of combustion of the shaft roaster through the hearth chamber, thereby imparting heat to the ore undergoing heating on the hearths, and mingling the gaseous products of the entire roasting operation.

19. The process of roasting finely divided zinc sulfide ore customarily requiring the application of extraneous heat to effect substantially complete desulfurization which comprises heating the ore in a bed heating operation in an atmosphere comprising the gaseous combustion products of the succeeding roasting stage to such an extent that the temperature of the ore is raised substantially to the ignition point, preheating an oxidizing gas flowing counter-current to the movement of the roasting ore.

20. Apparatus for roasting ores comprising a vertically disposed shaft roaster having an opening at the upper end thereof, a chamber mounted directly above the shaft roaster, an outlet for the chamber positioned immediately above the opening in the shaft roaster, a plurality of heating hearths in said chamber, means for feeding ore to the uppermost of said hearths, means for gradually passing ore while agitating the same successively over the hearths, means for gradually discharging ore from the lowermost hearth into the upper end of the shaft roaster in the form of a shower, a dust separator connected to the gas outlet of said chamber, means for passing oxidizing gas through said dust separator in heat exchange relation with hot combustion gases therein, whereby the oxidizing gas is preheated, means for passing upwardly through the shaft roaster a stream of. preheated oxidizing gas, whereby a suspension of the ore in the gas is formed, and means for passing the gaseous products of combustion of the shaft roaster through the hearth chamber, thereby imparting heat to the ore undergoing heating on the hearths, and mingling the gaseous products of the entire roasting operation.

THEODORE v. FOWLER, JR. 30 

